1. Field of the Invention
The present invention relates to a waste gate valve actuator for a turbocharger, and in particular to a waste gate valve actuator for a turbocharger having a fabricless diaphragm with certain other unique and advantageous properties.
2. Background
Turbochargers are commonly used with various types of engines for the purpose of providing a relatively high pressure charge of a fluid or gas, like air, to an internal combustion engine. The turbocharger operates in conjunction with the engine, typically by channeling engine exhaust gas from the engine into a rotateably driven compressor that in turn drives a compressor for compressing air or fluid for return to the engine. The return flow boosts the power of the engine, which among other things increases the flow exhaust gas to the turbocharger.
Thus, the speed of the turbocharger increases as the speed of the engine that it supports increases. This feedback loop can create an overload condition for either the turbocharger or the engine. In other words, safe operation of the engine and turbocharger requires a mechanism for the controlled release of pressure under extreme operating conditions to prevent damage to the system. The prior art teaches the use of a variety of devices to limit the rotational capacity of the turbocharger compressor, and thereby the amount of boost provided to the engine by the turbocharger. These devices include compressor inlet control valves, turbine bypass mechanism, blow-off valves, and waste gate valves. In each case the operation of the various devices includes the use of a pressure selective device divert some portion of the exhaust gas that drives the turbocharger to an alternative passageway.
In particular, waste gate valves open and close a passage way that diverts some portion of the exhaust gas away from the turbine or compressor. Thus, under load conditions that approach excessive levels a sufficient portion of the exhaust gas that drives the turbine flows through a bypass route thereby interrupting the feedback loop to avert dangerous operating conditions. In this manner, the boost pressure that the turbocharger provides to the engine is capped at predetermined maximum level to avoid damage to the engine or turbocharger.
Waste gate valves are controlled by a waste gate valve actuator, which is designed to open and/or close the valve under certain predetermined conditions. The actuator typically includes a housing that surrounds a pressure driven piston and depending rod, the motion of which opens and closes the waste gate valve. A resilient diaphragm is flexibly captured within interior of the housing. An inlet pressure source provides pressure to the actuator in proportion to the pressure levels of the exhaust gas that feeds the turbocharger. A spring provides selective resistance to the pressure and under normal conditions biases the diaphragm to a position that closes the bypass route. When the pressure builds to a maximum predetermined level during heavy load conditions, the pressure in the actuator overcomes the biasing force of the spring and displaces the diaphragm a sufficient distance to move the piston and rod enough to trigger the waste gate valve to allow the diversion of some portion of the exhaust gas.
In operation, the waste gate actuator undergoes substantial stress due to the nature of the conditions under which the turbocharger operates. In addition to the normal wear and tear associated with engines, the exhaust gases have corrosive properties that tend to deteriorate the diaphragm. Another important source of stress particularly on waste gate actuator diaphragms comprises operational vibration. Vibration can cause the edges of the diaphragm nearest to the housing to prematurely wear through contact between the diaphragm and the housing. Perhaps even more importantly, the repetitive operational displacement of the diaphragm comprises a substantial influence on the deterioration and subsequent failure of diaphragms. Thus, the diaphragm must both be flexible and durable, which has proved a troublesome combination for prior art designs. In particular, many prior art diaphragms for waste gate actuators are comprised of a combination of a proprietary fabric material like Nomex(copyright) and a thermoplastic or rubber material. The former provides flexibility while the latter provides durability. However, in practice even this design is subject to failure through repetitive use. Also, the combination is expensive and difficult to manufacture due to the combination of the two materials and the expensive of the woven fabric like materials. Other prior art attempts to improve the useful life of waste gate actuator diaphragms include increasing the thickness to improve durability, however, this comes at the expense of flexibility. In addition, some prior art diaphragms selectively vary the thickness of the diaphragm in order strengthen those portions that are most susceptible to failure. This approach, however, increases the cost and difficulty of manufacture.
Thus, a need exists for an improved diaphragm for a turbocharger waste gate valve actuator.
An object of the present invention comprises providing a waste gate valve actuator for use with a turbocharger having a flexible and durable thin non-fabric diaphragm substantially uniform in thickness.
These and other objects of the present invention will become apparent to those skilled in the art upon reference to the following specification, drawings, and claims.
The present invention intends to overcome the difficulties encountered heretofore. To that end, a waste gate valve actuator is provided for use with a turbocharger having a flexible and durable thin non-fabric diaphragm substantially uniform in thickness. The actuator comprises a cover and a bottom can joined at a crimp to the cover to form an interior cavity. A piston is located in the interior of the actuator comprising a piston cup located at an upper end and a rod depending downward to a lower end. A spring is captured between the piston cup and the bottom can for exerting a biasing force on the piston. Also provided is a non-fabric durable and flexible diaphragm of substantially uniform thickness, with a crimp end for air tight securement within the crimp, a top, and a convoluted side therebetween, wherein the diaphragm divides the interior of the actuator into an upper pressure chamber and a lower chamber at atmosphere with the piston located in the lower chamber. An air inlet introduces a pressurized substance into the pressure chamber whereby the introduction of a sufficient amount of the pressurized substance will exert sufficient pressure on the diaphragm to overcome the biasing force of the spring and force the piston downward a sufficient distance to actuate the waste gate valve of the turbocharger.